The present invention relates generally to restorative dentistry. More specifically, the invention relates to an implant abutment for dental restorations.
Restorative dentistry has made significant advances in the use of dental implants to support dental restorations intended to permanently replace natural teeth. Dental implants provide an alternative to removable dentures, fixed partial dentures, and single-tooth restorations.
In a jawbone anchored dental restoration, an implant of known design is surgically implanted into a patient's jawbone, leaving a gingival surface exposed. A support post, commonly referred to as an abutment, is then firmly fixed to the exposed surface of the implant. A dental prosthesis is secured to the abutment by means of a screw extending through a bore in the prosthesis and into a threaded bore in the abutment (screw retained) or via conventional cementation techniques (cement retained).
As described, for example, in U.S. Pat. No. 4,988,298 to Lazzara et al., the entire content of which is incorporated herein by reference, and as shown in FIG. 1, a dental implant restoration system 10 generally includes a dental implant 14, a support post or abutment 16, and a prosthesis 12. The implant is typically made from a biocompatible material such as titanium or titanium alloy, and is embedded into the jawbone leaving a gingival surface 22 flush or nearly flush with the gingival surface A-A of the jawbone. This gingival end includes an internally-threaded recess 24 and a multi-sided male projection for abutting with the abutment 16. The abutment 16 is securely attached to the lower or gingival end of the prosthesis 12 and functions to provide a rigid interconnection between the implant 14 and the prosthesis 12.
A passageway extends through the abutment 16 and provides a recess at the transgingival portion for engaging the projection of the implant. A screw 26 abuts against a shoulder 28 of the abutment and engages the threaded recess 24 of the implant to force a precision formed abutment surface 29 into seated contact with the gingival surface of the implant. The prosthesis 12 is fabricated around the upper portion of the abutment and may be connected to the abutment via screw 26 or cement. The prosthesis is colored to match the surrounding dentition.
Typically, the abutment is made of metal, such as titanium, and the prosthesis is fabricated from ceramic, a ceramic-based material such as porcelain, or a polymeric resin material. An entirely metallic abutment however, can be visible through the prosthesis, resulting in a dark, central rod-like shadow, particularly when exposed to bright light, which makes the prosthesis somewhat unattractive since it is distinguishable from a natural tooth. Various methods for preventing or masking the appearance of the shadow are known in the art.
One attempt to solve the attractiveness problem involves making a support post entirely of tooth-colored ceramic material. This approach allows direct surface bonding by interaction of a porcelain coping and/or prosthesis to the support post, resulting in a secure and almost seamless bond between the prosthesis and support post. While presenting an attractive alternative to the use of a titanium support post, the proposed solution presents a number of problems.
Ceramic materials generally have a much greater hardness than titanium. When an all-ceramic support post is used, inevitable rocking of the support post due to, for example, chewing, causes a high stress interaction between the metal implant and the ceramic material of the post. Since a ceramic support post is of greater hardness than a titanium implant, it can and does cause damage to the implant. If sufficient damage is caused, eventual surgical intervention is required to remove and replace the titanium implant. In addition, ceramic material is typically not radiopaque, and when using conventional x-ray imaging to examine the juncture between the abutment and the titanium implant, the interface between the two elements is not readily viewable and adequate examination cannot be conducted. Moreover, fracture of the all-ceramic post is also a consideration.
Recognizing the benefits of a metallic support, U.S. Pat. No. 5,685,714 to Beaty et al. describes an abutment having two distinct sections. As seen in FIG. 2, abutment 12 includes an inner section, or core 36, made from titanium or a titanium alloy and an outer section, or cuff 34, made from ceramic, typically aluminum oxide. The metallic core 36 provides the necessary strength to the abutment and provides a framework for connecting prosthesis 38 to implant 40. The ceramic cuff 34 preferably surrounds the entire exterior surface of the core 36, and shields the shadow of the metallic core 36 through the prosthesis 38. PureForm™ (Centerpulse Dental Inc., Carlsbad, Calif.), for example, is a tooth-shaped abutment composed of a titanium core and a ceramic cuff made of an alumina/zirconia blend. Screw-retained alumina or zirconia/alumina based abutments are available under the trademarks Bio-Cera™ (Bio-Lok International, Inc., Deerfield Beach, Fla.), CerAdapt™ (Nobel Biocare™ AB, Goteborg, SE) and ZiReal™ Post (Implant Innovations, Inc., Wilmington, Del.).
U.S. Pat. No. 6,497,573 to Wagner et al. describes a three part dental abutment that includes a shield between a metallic core and a polymeric cuff. The shield is preferably formed of an opaque material, such as a mixture of several mono and dimethacrylates, and may include various pigments to provide a variety of colors to best shield or mask any grayish or metallic color of the core.
U.S. Pat. No. 7,179,089 is directed to a two-part abutment having an upper section fabricated of a metal, zirconia or alumina cylinder and a shoulder attached to the cylinder and fabricated of a hybrid ceramic material, whereby a pigment may be added to the hybrid ceramic material to match the color of the patient's gum tissue.
Each of the aforementioned devices however, have certain drawbacks. The three part system is inherently more costly, both in time and materials. The two-part system of U.S. Pat. No. 7,179,089 requires the attachment of the cylinder to the shoulder component. Moreover, the two part systems, while effectively masking the shadow of the metallic core, result in the requirement for additional time and expertise in the fabrication of the prosthesis. When utilizing an entirely metallic abutment, the technician simply acknowledged the resulting appearance of the shadow and fabricated a prosthesis that matched the surrounding dentition. With the addition of a cuff component, however, the color of the cuff and the color of the prosthesis combine to create the color of the final restoration, and the technician must therefore take the color of the abutment into consideration when fabricating the prosthesis.
This is particularly important when the prosthesis is fabricated of ceramic. Since most ceramic restorations have inherent translucency, it is incumbent that the abutment be shaded so that it complements the desired shade of the restoration. This process is similar to determining the shade of a natural tooth prior to the fabrication of an all ceramic crown. In that case, it is recognized that the underlying natural tooth or “stump” will influence the shade of the final restoration.
U.S. Pat. Nos. 6,231,342 and 5,989,029 are directed to customized abutments and are hereby incorporated by reference. The abutments are customized by taking a series of measurements at the tooth site and fabricating an abutment based on the measurements. Although the abutments, are customized single-unit structures, there are no color and shade considerations.
Conventional abutments, such as PureForm™ Ceramic Coping (Centerpulse Dental Inc., Carlsbad, Calif.), Bio-Cera™ (Bio-Lock International, Inc., Deerfield Beach, Fla.), CerAdapt™ (Nobel Biocare™ AB, Goteborg, SE) and ZiReal™ (Implant Innovations, Inc., Wilmington, Del.), are typically available in one standard color chosen by the manufacturer, regardless of the material they are made from. Thus, an “exact match” between the abutment and prosthesis is not achieved. CerAdapt™ abutments for example, are available in Vita-Shade™ A-3 (Vita Shade™ Guide, Vident, Brea, Calif.).